there's a common misconception that open source, free software and FOSS, when referring to software (rather than to political stances), denote significantly different sets of software. there are rare exceptions that can be counted in one hand's fingers, but I suspect those are not the distinction you're making.
could you please point out what you mean by "not the same", as in, what difference you're getting at, so that it doesn't reinforce the misconceptions? (a common misconception is that only copyleft licensing, or only strong copyleft licensing, qualifies as free software, while lax permissive licenses don't; that's a misrepresentation that has been fed by propaganda)